Method of breaking ice

ABSTRACT

Injection of gas beneath ice sheets located in frigid waters to lift portions of the ice to place a stress on an area of ice for easier breaking by a vessel or marine structure. The gas conduits can be fixed as with a marine structure, or a movable flexible conduit for use with a vessel. Two mounds of ice can be created by injecting air at two locations to create a trough therebetween which is in stress for easier failure when contacted by the vessel or marine structure. An air motor or turbine can be used in the ends of the flexible conduits for moving the conduits outwardly from the vessel or the exhaust end of the conduit can be directed toward the vessel to utilize jetting action to push the conduit from the vessel. Connected bridles or hydraulic line actuated rudders can control direction so the conduits exhaust ends will properly position.

United -States Patent Bennett et al.

[ Oct. 15, 1974 METHOD OF BREAKING [CE [75] Inventors: John D. Bennett,Denton; Preston E.

Chaney, Dallas, both of Tex.

[73] Assignee: Sun Oil Company (Delaware), Dallas, Tex.

[221 Filed: Oct.2, 1970 211 A iwnnmsi Primary Examiner-Trygve M. Blix Wfi SSiSEQrlt Examiner lesus D. Sotelo Attorney, Agent, or FirmGeorge L.Church; Donald R. Johnson; John E. Holder [57] ABSTRACT Injection of gasbeneath ice sheets located in frigid waters to lift portions of the iceto place a stress on an area of ice for easier breaking by a vessel ormarine structure. The gas conduits can be fixed as with a marinestructure, or a movable flexible conduit for use with a vessel. Twomounds of ice. can be created by injecting air at two locations tocreate a trough therebetween which is in stress for easier failure whencontacted by the vessel or marine structure. An air motor or turbine canbe used in the ends of the flexible conduits for moving the conduitsoutwardly from the vessel or the exhaust end of the conduit can bedirected toward the vessel to utilize jetting action to push the conduitfrom the vessel. Connected bridles or hydraulic line actuated rudderscan control direction so the conduits exhaust ends will properlyposition.

9 Claims, 5 Drawing Figures Pmimanww I 3.841.252

I N VEN TOR JOHN D. BENNETT ATTORNEY RESTO/V 5. CH NE) METHOD OFBREAKING ICE [BACKGROUND OF THE INVENTION This invention deals with theproblems caused by ice floating in frigid waters such as the ArcticIslands area. Currently there is high interest in exploring for anddeveloping natural resources in such areas. In the search for anddevelopment of petroleum from offshore areas, platforms have been usedwhich are supported on the floor of a body of water by rigid uprightmembers. Such platforms if located in the Arctic Islands area would beexposed to ice floes which float freely in the water and may be of sucha size and propelled at such a speed that the platform support memberswould be subjected to damage or destruction from the severe pressures.Additionally, the specially equipped SS Manhattan recently made a voyagethrough the Northwest Passage to determine if a vessel could be used fortransportation of hydrocarbons from areas in Alaska and encountereddifficulty in penetrating the ice. Other vessels will be attempting toserve both the offshore drilling structures and storage facilities inthese areas and must be able to penetrate through ice floes in order toreach these locations.

The Arctic Ocean adjacent the North Slope area of Alaska is typical ofconditions a vessel or marine structure might encounter. This area ischaracterized by its shallow depth and gradual slope to deep water. Airtemperatures usually range from 40F. to +50F. The water is very uniformin temperature, from +28F. to +30F., and very saline except in thelagoons opposite the rivers. Winds are predominantly from the East, mph,with a maximum of 50 to 60 knots, however, waves are not usually morethan 5 feet high. In the months of November through April, large massesof ice are in continuous movement by the effects of wind in the ArcticOcean. Ice fields measuring thousands of feet in diameter are propelledin many directions by the winds and are generally unaffected by theminor currents present in the Arctic Ocean.

The main ice form in the Arctic Ocean is the ice sheet, which isgenerally uniform and 6 to 10 feet in thickness. Another form of iceencountered is rafted ice, which is the term used to describe theoverlapping of ice sheets as one sheet rides up over another sheetresulting in an ice floe made up of two or more distinct layers. In openlocations, the rafting does not generally take place between sheets ofmore than one or two feet in thickness, since thick sheets cannotwithstand the deflection necessary for one sheet to ride over the other.Rafted ice has a much smaller surface area than that of the moreprevalent ice sheets, and is not as strong because of poor bondingbetween its layers.

Other forms of ice in the Arctic Ocean are the icebergs and pressureridges. Icebergs do not occur, except in waters over 120 feet in depth.Since these icebergs can be several square miles in area, and can be upto 160 feet thick, in those areas where icebergs may be encountered, anabove water surface platform would not appear to be feasible. Pressureridges occur when two sheets of ice impinge upon each other. Crushingoccurs and the ice is broken and piles up above and below the generalice level. Pressure ridges may be encountered which are some 150 feetthick. These ridges should also be avoided.

Thus, it can be seen that offshore platforms located in shallow waterwill encounter ice sheets from 6 to 10 feet thick when located in theArctic Ocean, and occasionally rafted or sheet ice up to 15 feet thick.Generally speaking then, an offshore platform should be able toroutinely withstand at least 15 foot thick ice sheets having diametersof several thousand feet, being moved by winds of 15 mph. This ice has ashear strength of 60 psi and a crushing stregth of 300 psi.

Regarding ice which a vessel will encounter while attempting to servicedrilling platforms located in the Arctic Ocean as well as storagefacilities located in such areas as Cook Inlet and Prudhoe Bay, it ispresumed that ice would not be encountered beyond the same 10 or 15 footthick sections. It is therefore an object of the present invention toprovide a method and apparatus for aiding vessels to penetrate, andmarine structures to withstand, ice floes.

SUMMARY OF THE INVENTION With these and other objects in view, thepresent invention contemplates injecting a fluid such as a gasunderneath an ice sheet to raise portions thereof in order to place anarea of the ice sheet in stress. The gas is injected at locations whichwill provide a stressed area in the ice sheet in the path of a vesselfor easier breaking of the ice or to provide a stressed ice area whichcontacts a marine structure. The gas is injected by conduits which arein fixed locations for marine structures, and are flexible, positionableconduits for use with vessels. The conduits may be motivated by gaspropulsion and maneuvered by hydraulic actuated vanes, connectedbridles, or other known control mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a vesselhaving apparatus for introducing a gas beneath an ice sheet;

FIG. 2 is a cross-sectional view of the sheet of ice deformed by theintroduced gas;

FIGS. 3A and 3B are cross-sectional and plan views respectively of thedischarge ends of gas conduits which incorporate propulsion systems forpositioning the conduits; and

FIG. 4 is a plan view of a marine structure encircled by gas conduits.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1,there is seen a vessel 20 located in the midst of an ice sheet 50.Extending from the vessel 20 are a pair of conduits 24 which are shownto be laterally spaced from one another. These conduits 24 are connectedto pump 22 and extend through guides 36. When the vessel 20 firstencountered the ice sheet 50, these conduits 24 were extended from thevessel 20 and positioned in a manner which will hereinafter hediscussed. Once the conduits are positioned, gas is pumped through theconduits 24 by pump 22 to elevate ice portions 16 and points A and B areapproximately the center of such elevated ice portions. Located betweenelevated ice portions 16 is a depressed area generally defined by lines18. The area between lines 18 has been forced downward in reaction tothe upward movement of the ice portions 16. As the vessel 20 movesforward, and contacts the ice sheet 50, a portion of the weight of thevessel is applied to the ice sheet at point B which tends to split theice down the middle along the line D-E. As the ice sheet 50 is forceddownward, the edge of the ice sheet along the lines E-I-I and EJ wouldbe forced downward since the load on the ice sheet 50 is greater alongthe side of the ice sheet adjacent the vessel 20, than it is on theopposite side of the elevated ice portion 16. Thus, these elevatedportions should continue to move forward with the same velocity that thevessel 20 moves along the line D-E. Therefore, as a vessel encountersice sheets in Arctic regions, conduits are extended from the vessel andlaterally spaced in front of the vessel under the ice sheet. Gas ispumped through the conduits to elevate two mounds in the ice with aresultant stressed depressed area therebetween. This area is thencontacted by the vessel, whose weight more easily breaks the ice sheetbecause of its weakened condition due to the stressing caused by the airbubble. The conduits can be retracted for operation of the vessel inclear water or waters having thin ice sheets.

FIG. 2 illustrates the deformity of the ice sheet 50 relative to thenormal water level 12. As gas is injected through the conduits 24 asshown in FIG. 1, it raises the ice sheet 50 and occupies the area 28below points A and B. As points A and B are elevated, point C locatedbetween A and B is depressed. This deformation of the ice sheet 50places point C in stress and enables the vessel 20 shown in FIG. 1 tomore easily break the ice sheet 50 when the weight and moving force ofthe vessel bow is applied to point C.

FIGS. 3A and 3B show alternative embodiments for moving the conduitdischarge ends outwardly from the vessel 20. FIG. 3A illustrates aconduit 24 terminating such that the discharge openings are directedtoward the vessel. Thus, when air or other fluid mediums are injectedthrough conduits 24 and exit the discharge opening 26, the jettingaction of the medium forces the discharge end of the conduit away fromthe vessel. Assuming the conduit is a telescoping member, made of aflexible material or the like, such force will move the discharge end ofthe conduit away from the vessel. Fixed vane member 56 is located on theterminal end of the conduit 24 so that water moving relative to the vanemember will force the conduit discharge end in a counter clockwisedirection. Attachment loop 58, preferably made of metal, as is thedischarge end of conduit 24, is positioned, adjacent the vane member 56and in operation is attached to a flexible connector member which hasnot been shown. The co-action between the vane member 56 and connectormember attached to loop 58 operates to position the discharge end of theconduit 24 as will be explained hereinafter.

FIG. 3B illustrates conduit 24 with a fluid motor located in the endthereof. As fluid proceeds through conduit 24, it contacts vanes locatedin the conduit which rotate shaft 52 on the end of which is propeller30. The shaft 52 rotates on bearings and the propeller 30 is guarded byshroud 32 so as not to be fouled by floating objects. After the fluidmedium proceeds through the vanes it exits apertures located on eachside of the conduit and located generally at 26. The propeller 30 isoperated to pull the conduit 24 away from the vessel.

Several methods can be utilized for directionally controlling theconduit discharge ends so that they will be located under an ice sheetso as to provide a stressed trough between elevated portions of the icesheet. One such system is the use of a hydraulic line located inside theconduit 24 which acts on a vane member located at the discharge end ofthe conduit. Pressure applied through the hydraulic line controls thevane member such that the discharge end of the conduit 24 can readily bepositioned. Sound sensors can be used to de termine the location of theconduit discharge ends when it is hidden by the ice sheet, or water.This system of positioning has not been shown in the drawings. Anothermethod of positioning the conduit discharge ends is to tie two conduits24 with a flexible connection of such length as to provide the properlateral distance for the purposes of ice sheet elevation in FIG. 3A.Vanes attached to the discharge ends of the conduits 24 can be arrangedto pull the discharge end in an outward direction to keep the flexibleconnection in tension. The flexible connectors are attached to eachconduit at attachment loops 58. Upwardly directed vents at the dischargeend of the conduis 24 could be used to force the ends of the conduitsdownward so that the flexible connecting element would not become fouledon an anomaly on the underside of the ice sheet. This upwardly directedvent should be constructed to operate only when extremely high injectionrates of gas are used so that the conduit discharging ends would diveonly atsuch times as are desired.

FIG. 4 illustrates an offshore marine structure 54 atop a support member48. Extending away from the marine structure 54 are fixed conduits 42which extend outwardly to upwardly directed pipes 40. Pump and controlpanel 44 communicates with the fixed conduits 42. In operation, sensorsand/or visual observations can be used to determine the direction of anencroaching ice floe. Once this is determined, a pair of directed pipes40 are selected to emit a gaseous element for the purpose of creatingelevated portions of the ice. These upwardly directed pipes 40 areselected so that the lateral distance therebetween will provide a trougharea in the ice floe which will impinge against the marine structuresupport member 48. Since this depressed area of the ice floe is undertension, it becomes very easy to shear by the support member 48. Thefixed conduits 42 may be rigid pipe members and the upwardly directedpipes 40 may be placed so that they extend upward so that they arefairly close to the ice floe, or may be dispensed with entirely, and anaperture in the fixed conduits 42 may be used instead.

While particular embodiments of the present invention have been shownand described, it is apparent that changes and modifications may be madewithout departing from this invention in its broader aspects, andtherefore, the aim in the appended claims is to cover all such changesand modifications as fall within the true spirit and scope of thisinvention.

What is claimed is:

1. Method of breaking ice sheets floating on a body of water comprisingthe steps of: injecting a gas under the ice sheet at two locations tocreate two spaced raised portions of the ice sheet and a resultantstressed depressed ice area therebetween; and applying a force to thestressed depressed area of ice to fracture the ice sheet.

2. The method of claim 1 wherein the gas is injected from a vessel andthe ice sheet is in the path of the vessel, and wherein the stresseddepressed ice area is created in the path of the vessel and the icesheet is fractured by moving the vessel against the stressed depressedice area.

3. The method of claim 2 wherein the gas is injected through flexibleconduits attached to the vessel having gas motors in the discharge endsof the flexible conduits and including the step of passing a gas fromthe vessel through the flexible conduits and the gas motors so as toposition the discharge ends of the conduits laterally and forward of thevessel.

4. The method of claim 3 including the steps of monitoring the locationof the discharge ends of the flexible conduits and controlling movementof the conduit to position the discharge ends at a desired location.

5. In a method of breaking ice in the path of a vessel I from a largerice mass by applying the weight of the vessel to the ice mass to forceit downwardly and thereby break a section of ice therefrom, theimprovement comprising: injecting a gas beneath the ice mass to createtwo mounds in the ice mass spaced laterally and forward of the vessel,thereby creating a stressed depressed area between said mounds; andthereafter applying the weight of the vessel to the stressed depressedarea.

6. A method of breaking ice from an ice mass in the path of a vesselcomprising the steps of: extending a pair of conduits from the vessel sothat the discharge ends are spaced laterally beneath the ice mass andare forward of the vessel; pumping a gas through and out the dischargeend of the conduit thereby elevating two areas of the ice mass intomounds thereby stressing and depressing the area between the mounds; andmoving the vessel forward against the depressed area to fracture the icemass.

7. The method of claim 6 wherein conduits are constructed so that gasforced through the conduit will act as a force to move the conduitdischarge end away from the vessel.

8. Apparatus for breaking ice floating on a body of water adjacent amarine structure including: a pump mounted on the marine structure; aplurality of elongated conduit means extending from said structure andspaced completely around said structure and having laterally spacedterminal ends; discharge means on said terminal ends arranged to pass agas from said conduits; and means for directing a gas through a selectedpair of conduit means.

9. Apparatus for breaking ice floating on a body of water including: apump mounted on a self-propelled vehicle; at least two elongatedconduits, made of a flexible material, extending from said vessel havinglaterally spaced terminal ends, which terminal ends includes means formoving the terminal ends of the conduits relative to the vessel, whichterminal ends moving means conduits.

1. Method of breaking ice sheets floating on a body of water comprisingthe steps of: injecting a gas under the ice sheet at two locations tocreate two spaced raised portions of the ice sheet and a resultantstressed depressed ice area therebetween; and applying a force to thestressed depressed area of ice to fracture the ice sheet.
 2. The methodof claim 1 wherein the gas is injected from a vessel and the ice sheetis in the path of the vessel, and wherein the stressed depressed icearea is created in the path of the vessel and the ice sheet is fracturedby moving the vessel against the stressed depressed ice area.
 3. Themethod of claim 2 wherein the gas is injected through flexible conduitsattached to the vessel having gas motors in the discharge ends of theflexible conduits and including the step of passing a gas from thevessel through the flexible conduits and the gas motors so as toposition the discharge ends of the conduits laterally and forward of thevessel.
 4. The method of claim 3 including the steps of monitoring thelocation of the discharge ends of the flexible conduits and controllingmovement of the conduit to position the discharge ends at a desiredlocation.
 5. In a method of breaking ice in the path of a vessel from alarger ice mass by applying the weight of the vessel to the ice mass toforce it downwardly and thereby break a section of ice therefrom, theimprovement comprising: injecting a gas beneath the ice mass to Createtwo mounds in the ice mass spaced laterally and forward of the vessel,thereby creating a stressed depressed area between said mounds; andthereafter applying the weight of the vessel to the stressed depressedarea.
 6. A method of breaking ice from an ice mass in the path of avessel comprising the steps of: extending a pair of conduits from thevessel so that the discharge ends are spaced laterally beneath the icemass and are forward of the vessel; pumping a gas through and out thedischarge end of the conduit thereby elevating two areas of the ice massinto mounds thereby stressing and depressing the area between themounds; and moving the vessel forward against the depressed area tofracture the ice mass.
 7. The method of claim 6 wherein conduits areconstructed so that gas forced through the conduit will act as a forceto move the conduit discharge end away from the vessel.
 8. Apparatus forbreaking ice floating on a body of water adjacent a marine structureincluding: a pump mounted on the marine structure; a plurality ofelongated conduit means extending from said structure and spacedcompletely around said structure and having laterally spaced terminalends; discharge means on said terminal ends arranged to pass a gas fromsaid conduits; and means for directing a gas through a selected pair ofconduit means.
 9. Apparatus for breaking ice floating on a body of waterincluding: a pump mounted on a self-propelled vehicle; at least twoelongated conduits, made of a flexible material, extending from saidvessel having laterally spaced terminal ends, which terminal endsincludes means for moving the terminal ends of the conduits relative tothe vessel, which terminal ends moving means comprises propulsion meansactivated by a gas operated motor means; and discharge means on saidterminal ends arranged to pass a gas from said conduits, wherein saidpump supplies gas under pressure to said conduits.